1. Field of the Invention
This invention relates generally to an apparatus for determining the center of a hole and, more particularly, to an extension for use with an offset indicator so as to permit location of the center of deep holes, the center of hard to get at holes or surface irregularities in difficult to reach places.
Offset indicating tools of the type manufactured by Interrapid of Switzerland are used in conjunction with milling machines such as jig borers, boring mills, etc. These offset indicators may be used, for example, to locate the center of a hole or measure surface irregularities and consist generally of a pivotable handle assembly, an indicator dial, a pivotable ball point needle, and linkage coupled between the needle and the indicator dial for transmitting needle movememt to the indicator dial. Such a tool, properly positioned at the center of a hole will register zero on the indicator dial as the tool is turned causing the ball point to travel across the inner surface of the hole. If the tool is not positioned in the center of the hole, the needle will be forced to pivot as the point rides along the inner surface of the hole resulting in reading on the indicator dial which is indicative of the degree to which the tool is off center.
It is often necessary to make measurements such as locating the center of a hole in difficult to reach areas. This problem has been solved in two ways. First, the entire offset indicator tool has been made longer in order to increase its reach. Such lengthened tools are significantly more expensive and are much less versatile. Second, the standard ball point needle has been replaced by a longer needle. While not as expensive as the first solution, the indicator readings generated by a tool modified in this manner are no longer accurate representations of offset.